Lexi Minetree is the newcomer stepping into Elle Woods. She plays a young Elle in “Elle,” the “Legally Blonde” prequel series arriving July 1 on Prime Video. Reese Witherspoon is an executive producer, so the dress wasn’t a coincidence or a vintage find. It was a handoff. The actress who built the character watched the actress who’s inheriting it wear the dress that started the whole thing. Lexi Minetree, cast as young Elle Woods in the upcoming…